Try this:

// set background color for 'Height' to the dark gray [0.2,0.2,0.2]
heightInput.graphics.backgroundColor 
  = heightInput.graphics.newBrush(heightInput.graphics.BrushType.SOLID_COLOR,[0.2, 0.2, 0.2]);

// text color for 'Height' to white [1,1,1]
heightInput.graphics.foregroundColor
  = heightInput.graphics.newPen(heightInput.graphics.PenType.SOLID_COLOR, [1,1,1], 1);

But UI can work differently in some versions of Illustrator. I just tested it in my CS6/Win10 and it seems work.

More information is here: https://creativepro.com/files/kahrel/indesign/scriptui.html

Full code:

var w = new Window ("dialog");

var text_color = [1,1,1];
var bg_color = [.2,.2,.2];

w.alignChildren = ["fill","fill"];
w.preferredSize = [150, 250];
w.inputBox = w.add('panel', undefined, "Input Box");

w.inputBox.add('statictext{text: "Height: "}');

var heightInput = w.inputBox.add('edittext {characters: 12, active: true}');
heightInput.graphics.foregroundColor = heightInput.graphics.newPen(heightInput.graphics.PenType.SOLID_COLOR, text_color, 1);
heightInput.graphics.backgroundColor = heightInput.graphics.newBrush(heightInput.graphics.BrushType.SOLID_COLOR,bg_color);

w.inputBox.add('statictext{text: "Width: "}');

var widthInput = w.inputBox.add('edittext {characters: 12, active: false}');
widthInput.graphics.foregroundColor = widthInput.graphics.newPen(widthInput.graphics.PenType.SOLID_COLOR, text_color, 1);
widthInput.graphics.backgroundColor = widthInput.graphics.newBrush(widthInput.graphics.BrushType.SOLID_COLOR,bg_color);

w.inputBox.add('statictext{text: "Spine: "}');

var spineInput = w.inputBox.add('edittext {characters: 12, active: false}');
spineInput.graphics.foregroundColor = spineInput.graphics.newPen(spineInput.graphics.PenType.SOLID_COLOR, text_color, 1);
spineInput.graphics.backgroundColor = spineInput.graphics.newBrush(spineInput.graphics.BrushType.SOLID_COLOR,bg_color);

w.inputBox.add('statictext{text: "Joint: "}');

var jointInput = w.inputBox.add('edittext {characters: 12, active: false}');
jointInput.graphics.foregroundColor = jointInput.graphics.newPen(jointInput.graphics.PenType.SOLID_COLOR, text_color, 1);
jointInput.graphics.backgroundColor = jointInput.graphics.newBrush(jointInput.graphics.BrushType.SOLID_COLOR,bg_color);

var okBtn = w.add("button", undefined, "Draw");

w.show();

Win10 / CS6:

MacOS High Sierra / CC 2014 (18.0.0)